Only snap on key _downs_ (#6517)

## Summary of the Pull Request
Prior to #6309, we'd only snap on input for non-modifier key_down_ events. #6423 fixed this for modifier keys, but didn't fix this for keyups.

## References
* #6423 was an incomplete fix to this problem, which caused this regression

## PR Checklist
* [x] Closes #6481
* [x] I work here
* [ ] Tests added/passed
* [n/a] Requires documentation to be updated

src/cascadia/TerminalCore/Terminal.cpp

@@ -419,7 +419,9 @@ bool Terminal::SendKeyEvent(const WORD vkey,
 {
     // GH#6423 - don't snap on this key if the key that was pressed was a
     // modifier key. We'll wait for a real keystroke to snap to the bottom.
-    if (!KeyEvent::IsModifierKey(vkey))
+    // GH#6481 - Additionally, make sure the key was actually pressed. This
+    // check will make sure we behave the same as before GH#6309
+    if (!KeyEvent::IsModifierKey(vkey) && keyDown)
     {
         TrySnapOnInput();
     }